Oil is typically supplied to hydraulic valve lifters through conduits in the cylinder head. Oil can drain out of each valve lifter between the valve lifter body and plunger into these conduits (i.e., back-flow) during engine shutdown. If, during engine shutdown, a sufficient amount of oil drains out of the valve lifters and out of the conduits (thereby limiting the amount of oil which can be instantaneously supplied to the valve lifters), noise can result during start-up of the engine. Pressure regulators or check valves can be used to obstruct back-flow of the oil out of the valve lifters and conduits during engine shutdown.